Radio and/or optical propagation paths are influenced by atmospheric refractivity in a manner that is often difficult to characterize and/or predict. Refractive gradients in the atmosphere due to the structure of temperature and water vapor fields can cause reflective layers that can duct or trap propagation. Optical mirages are the result of refractive gradients that cause upward bending thus precluding views of the surface at distances from the observer. Horizontal gradients in refractivity influence astronomical observations, celestial navigation, radar tracking of orbiting and other objects in flight, and other pointed observations.
Such atmospheric effects can preclude or divert propagation such that sources or receivers are hidden from view. On the other hand, ducts can create propagation paths that follow the curvature of the earth, thus enabling visibility or radio propagation over longer than normal distances. Ducting is most prominent over the oceans and can, for instance, either make vessels visible to radar at greater than normal ranges or, alternatively, make radar detection impossible, hiding surface hugging missiles or aircraft from detection. Long range radio communications are also subject to ducting and other effects of refractivity, and short radio links such as those associated with cellular communications can also be affected.
The ability to gauge and predict atmospheric refractivity would therefore be useful, and could be applied to enhance stealth and security as well as for improving communications, detection and/or observations of various types.
It has been suggested heretofore that microwave radiometer receivers, capable of determining the amount of atmospheric emission across spectral wavebands, can be used for profiling atmospheric temperature and moisture and, base thereon, predicting various parameters related to weather conditions (see U.S. Pat. Nos. 6,377,207, 6,308,043, 5,526,676 and 4,873,481). Adaptation of such receivers and systems for use in the field of atmospheric refractivity characterization and prediction has not been heretofore suggested, however, and could be utilized.